1. Field of the Invention
The present invention relates to stable ascorbic acid compositions or formulations and methods of use. More particularly, the invention relates to novel, micronized L-ascorbic acid (vitamin C) compositions for topical application, said compositions having a pH that is basic relative to the pH of skin, and being useful as collagen production stimulators, as antioxidants and/or as ultraviolet (UV) protectants.
2. Description of the Related Art
Ascorbic acid (vitamin C) and its derivatives are not endogenously produced and must be obtained from dietary sources. Ascorbic acid is a major cellular antioxidant and is known to promote collagen expression, wound healing and, when applied topically, is capable of protecting the skin against ultraviolet (UV) light exposure, although it is not a sunscreen. See, e.g., Colvon, R. M. & Pinnell, S. R., “Topical Vitamin C in Aging” in Clinics in Dermatology, Skin Aging, and Photoaging, Antonio Ledo. ed., 14 227–234 (1996); Shindo et al., J. Invest. Dermatol., 102, 470–75 (1994); Freiberger, H. et al., J. Invest. Dermatol. 75, 425–30 (1980). However, ascorbic acid, and particularly L-ascorbic acid, is unstable in currently commercially available pharmaceutical vehicles for topical delivery to the skin. This instability leads to loss of potency and discoloration which may be due to oxidation of the L-ascorbic acid. In addition, L-ascorbic acid tends to hydrolyze when exposed to water, so is not stable in aqueous formulations or aqueous delivery vehicles.
Currently commercially available, topical L-ascorbic acid formulations therefore have associated disadvantages including, for example, instability, insufficient or less than optimal L-ascorbic acid concentrations, and the need for relatively low pH, typically from approximately 2.0 to approximately 3.0, which is acidic relative to the typical pH of skin, which is approximately 4.5 to approximately 5.0. Such low pH formulations promote skin irritation and require the presence of significant amounts of water, the presence of which tends to limit the ability of the ascorbic acid formulation to penetrate the skin.
There is, accordingly, a need for a stable topical ascorbic acid formulation which has sufficient ascorbic acid concentration, exhibits good skin penetration and is non-irritating. The present invention provides such formulations in a variety of embodiments.